Transparent conductors are utilized on touch screens to enable human touch or gesture interactions with computers, smart phones, and other graphics-based screen interfaces. Touch screen devices can be made by patterning (e.g., printing) a conductive material into electrical traces on a flexible substrate. Patterning of the conductive material can be performed in a roll-to-roll process where the substrate is unwound, converting operations such as printing and drying/curing are performed, and then the patterned substrate is wound again into a roll for further transport and processing. The patterned conductive layers can be connected to electronic circuit components such as, for example, flexible circuits, to form an electronic touch sensor that can be used as a component of an electronic device.
There are several approaches to patterning the conductive materials for use in electronic assemblies such as, for example, touch sensors.
In one example, the conductive material can be printed directly to form a pattern from a dispersion or ink, using standard printing processes such as, for example, ink-jet, gravure, flexographic, or screen printing. This direct printing technique produces a pattern in one step, with minimal waste. However, variations in the print thickness due to defects such as ribbing and pinholes may produce unacceptable variations in conductivity, as well as negatively impacting the optics of the sensor.
In another example, the surface of the substrate can be uniformly coated with the conductive material by forming a substantially continuous conductive layer. A resist material is then printed on the conductive layer using printing processes such as, for example, flexographic printing, gravure printing, ink jet printing, screen printing, spray coating, needle coating, photolithographic patterning, and offset printing. The patterned resist material allows selective removal of portions of the conductive layer to create a desired pattern (subtractive patterning). Selective removal is often accomplished either by wet chemical etching or laser ablation.
In some manufacturing processes, patterns of material may be deposited on the flexible substrate in layers through multiple deposition steps. Some articles require that the patterns be precisely registered on one or both sides of the substrate. To achieve accurate registration between the layers, lateral (cross web) positioning and longitudinal (down web) positioning must be maintained as the substrate moves through multiple manufacturing steps. Maintaining registration between layers formed on the substrate becomes more complex when the substrate is flexible or stretchable, and the patterns are made smaller and more intricately detailed. Various methods have been employed to improve the accuracy of these registration steps such as, for example, edge detection and the printing of fiducial marks.
In some fabrication processes, layers of conductive material are patterned, with each patterned layer separated by an insulating material. To make electrical connections to and between the conductive patterned layers in such a multi-layer construction without forming short-circuits, it can be important to create and maintain a reliable conductive path, generally referred to as a via, between the non-adjacent patterned conductive patterned layers. However, precise registration between adjacent layers to form vias in a multi-layer construction can be difficult, time-consuming and expensive.